eth: request id dispatcher and direct req/reply APIs (#23576)

* eth: request ID based message dispatcher

* eth: fix dispatcher cancellation, rework fetchers idleness tracker

* eth/downloader: drop peers who refuse to serve advertised chains

p2p/peer.go

@@ -121,10 +121,18 @@ type Peer struct {
 
 // NewPeer returns a peer for testing purposes.
 func NewPeer(id enode.ID, name string, caps []Cap) *Peer {
+	// Generate a fake set of local protocols to match as running caps. Almost
+	// no fields needs to be meaningful here as we're only using it to cross-
+	// check with the "remote" caps array.
+	protos := make([]Protocol, len(caps))
+	for i, cap := range caps {
+		protos[i].Name = cap.Name
+		protos[i].Version = cap.Version
+	}
 	pipe, _ := net.Pipe()
 	node := enode.SignNull(new(enr.Record), id)
 	conn := &conn{fd: pipe, transport: nil, node: node, caps: caps, name: name}
-	peer := newPeer(log.Root(), conn, nil)
+	peer := newPeer(log.Root(), conn, protos)
 	close(peer.closed) // ensures Disconnect doesn't block
 	return peer
 }